1. Field of the Invention
The present invention relates to a power supply device having multiple outputs and supplying power to a light emitting diode (LED) and a control circuit thereof.
2. Description of the Related Art
Recently, in the field of displays, display devices using cathode ray tubes (CRT) have been replaced by flat panel display (FPD) devices reflecting consumer demand for features such as high resolution, large screens, and the like.
Particularly, in the case of large display devices, the use of liquid crystal display (LCD) devices has rapidly increased, due to advantages thereof in terms of lightness and slimness and such displays have come to play a leading role in the field of displays) in view of the cost and marketability thereof.
Meanwhile, in existing liquid crystal display (LCD) devices, cold cathode fluorescent lamps (CCFLs) have mainly been used as backlight light sources. However, recently, light emitting diodes (LEDs) have gradually come to be used as backlight light sources, due to various advantages thereof, such as low power consumption, a relatively long effective lifespan, environmental friendliness, and the like.
In order to drive a light emitting diode, a power supply circuit converting commercially-available alternating current (AC) power into direct current (DC) power and a driving circuit controlling the supplying of the DC power to the light emitting diode are generally used.
The power supply circuit may be classified as having a primary side and a secondary side, based on a transformer provided therein, in order to enhance an insulating function, wherein the primary side is configured of a circuit rectifying and smoothing the commercial AC power to switch the power, and the secondary side is configured of a circuit rectifying power transformed by the transformer and controlling a supply of the rectified power to a load.
That is, as disclosed in the following Related Art Document, generally, a power switching control circuit is formed on the primary side and the above-mentioned driving circuit is formed on the secondary side. In this configuration, in order to smoothly control switching of the power, information regarding a state of the power supplied to the light emitting diode should be feedbacked and the switching of the power should be controlled based on the information. To this end, a photo coupler having an insulating function to transfer a feedback current is mainly used. However, since the photo coupler is an optical device, signal transfer characteristics depend on photons, a use period, and a junction temperature, so that circuit design may be difficult and manufacturing costs increased due to the use of the photo coupler.
In order to solve these problems, the power switching control circuit and the driving circuit may be formed on the secondary side. However, in such a configuration using a scheme of receiving feedback information regarding a power state on the secondary side to control the switching on the secondary side, it is difficult to precisely control a switching frequency. Further, instead of not using the photo coupler, since a non-linear device such as a transistor for receiving and directly using the feedback information regarding the power state on the secondary side should be additionally used, manufacturing costs may still increase.